In what is generally known as half-engine operation of an internal combustion engine, half of the cylinders are deactivated by switching off the intake and discharge valves as well as the injection, which allows fuel to be saved in comparison with standard full-engine operation. As an alternative, the half-engine operation also may be realized by deactivating only the injections. However, it must be taken into account then that this causes fresh air to be pumped through the affected cylinders, so that a post-connected catalytic converter is no longer able to convert at an air/fuel ratio of λ=1. For this reason, half-engine operation realized by deactivating the injection for half of the cylinders is implemented only in a configuration where all cylinders of one cylinder bank to which a separate exhaust tract with its own catalytic converter is assigned are suppressed. The other cylinder bank is always fired in full.
The crankcase ventilation is usually implemented symmetrically on both cylinder banks. In half-engine operation, however, the crankcase ventilation must no longer take place on the suppressed cylinder bank since the catalytic converter assigned to the suppressed cylinder bank is no longer able to convert the oil and gas mist introduced by the crankcase ventilation, which could lead to an exceeding of the prescribed emission limits. Therefore, an actuator in the form of a shutoff valve is used, which is open in full-engine operation and usually enables a symmetrical feeding of the crankcase ventilation to the two cylinder banks. In half-engine operation, this shut-off valve is closed in order to route the crankcase ventilation only to the not suppressed, completely fired cylinder bank. Depending on the position of the shutoff valve, a different distribution of the crankcase ventilation to the two cylinder banks comes about.
Since the exhaust-gas composition in the two exhaust tracts of the cylinder banks is affected to different degrees depending on the position of the shutoff valve, it is desirable to diagnose the function of the shutoff valve.